Friction clutch

ABSTRACT

A friction clutch which is provided with a system to compensate for wear upon the friction linings of the clutch disc and, if necessary, for wear upon certain other parts employs one or more diaphragm springs or other energy storing elements which assist in the disengagement of the clutch so that the disengaging force is relatively low and/or that such force fluctuates within a relatively narrow range. The energy storing element or elements can operate in parallel with the clutch spring and can be installed between the housing of the friction clutch and the clutch spring. The disengaging force of the energy storing element or elements can be assisted by the bias of resilient segments between the friction linings of the clutch disc.

BACKGROUND OF THE INVENTION

The invention relates to clutches in general, and more particularly toimprovements in friction clutches. Still more particularly, theinvention relates to improvements in friction clutches which can beutilized with advantage in power trains between the engines and thewheels of motor vehicles.

A friction clutch of the type to which the present invention pertainsnormally employs a housing or cover which receives torque from the primemover of a vehicle, for example, by way of a counterpressure plate (suchas a flywheel) which is driven by the output element (e.g., a camshaftor a crankshaft) of a combustion engine. An axially movable pressureplate is installed between the housing and the counterpressure plate andis caused to bias a clutch disc against the counterpressure plate whenthe clutch is engaged. The clutch disc then transmits torque to theinput shaft of a transmission or another torque receiving part in thepower train of the vehicle. The means for biasing the pressure platetoward the counterpressure plate (to thus clamp the clutch disc betweenthe two plates in the engaged condition of the clutch) normallycomprises a clutch spring (particularly a diaphragm spring) which reactsagainst the housing and bears against the adjacent side of the pressureplate when the clutch is engaged. The pressure plate shares the angularmovements of the housing and of the counterpressure plate; to this end,the pressure plate is normally coupled to the housing by leaf springswhich permit the pressure plate to move toward and away from thecounterpressure plate in the direction of the common axis of the housingand the counterpressure plate but prevents the pressure plate fromturning relative to the housing.

It is further known to provide a friction clutch of the above outlinedcharacter with a unit which can compensate (preferably automatically) atleast for wear upon friction linings which form part of the clutch discand are in frictional contact with the pressure plate and thecounterpressure plate in the at least partially engaged condition of theclutch.

Friction clutches of the aforedescribed type are described and shown,for example, in published German patent application Serial No. 42 39 289as well as in the prior art which is referred to in such application.

An advantage of the wear compensating unit is that it renders itpossible to bias the pressure plate and the counterpressure plate of thefriction clutch against the adjacent friction linings of the clutch discwith a considerable force even after the friction linings have alreadyundergone extensive wear. Another purpose of the wear compensating unitis to render it more likely that the clutch can be disengaged inresponse to the application of a relatively small disengaging force,namely a disengaging force whose maximum value can be said to be withinan acceptable (relatively low) range, as well as to establishcircumstances under which the disengaging force is likely to remain atleast substantially constant during the useful life of the clutch. Theuseful life of the clutch is determined, to a considerable degree, bythe useful life of the friction linings on the clutch disc even thoughcertain other factors (such as the wear upon the pressure plate, thewear upon the counterpressure plate and/or the wear upon the clutchspring or springs) are also apt to affect the life expectancy of thefriction clutch.

The utilization of diaphragm springs as a means for biasing the pressureplate against the adjacent friction linings of the clutch disc in theengaged condition of the friction clutch has been found to exhibit theadvantage that the clutch can be disengaged in response to theapplication of a relatively small (maximum) disengaging force and thatthe disengaging force need not fluctuate within a relatively wide range.The nature and the mounting of the diaphragm spring (which serves tobias the pressure plate against the clutch disc in the engaged conditionof the friction clutch) are such that the magnitude of the force beingapplied by the diaphragm spring decreases at least during the major partof the distance that must be covered by the pressure plate for thepurpose of disengagement of the clutch, i.e., the diaphragm springexhibits a degressive force-to-distance characteristic.

However, the aforedescribed conventional friction clutches also exhibitcertain serious drawbacks. Thus, even if the means for engaging theclutch employs one or more diaphragm springs, the magnitude of thedisengaging force which must be applied in order to move the pressureplate away from the clutch disc often varies within an excessively widerange. As a rule, the disengaging force which must be applied to movethe pressure plate away from the counterpressure plate at first risestoward an undesirably high maximum value to thereupon gradually decreaseto a minimum value. The difference between the maximum and minimumvalues of such disengaging force is considerable and, in many instances,well above the acceptable range. As a rule, the ratio of the maxima andminima of disengaging forces which must be applied in heretofore knownfriction clutches of the above outlined character is between 1.5 and 2.5or even higher.

The need for the application of very pronounced disengaging forces isundesirable irrespective of whether the clutch is being manipulated bythe operator of the vehicle or automatically, e.g., by a servomotor. Ifthe clutch is to be disengaged by a motor, the dimensions of such motorare proportional to the magnitude of the disengaging force which is tobe applied in order to move the pressure plate away from thecounterpressure plate. The same applies for the energy requirements ofthe motor. Moreover, it is necessary to employ stable and hence bulkyand more expensive means for transmitting motion in order to disengagethe clutch. Rather bulky, heavy and expensive motion transmitting meansare necessary on the additional ground that such parts must withstandpronounced deforming stresses during transmission of large forces fromthe disengaging motor to the pressure plate in order to disengage theclutch. Even the elasticity of the motion transmitting parts must belimited to a minimum in order to ensure predictable disengagement of theclutch against the opposition of the diaphragm spring(s).

OBJECTS OF THE INVENTION

An object of the invention is to provide a friction clutch which isconstructed and assembled in such a way that it can be disengaged inresponse to the application of relatively small forces.

Another object of the invention is to provide a friction clutch whichcan be disengaged in response to the application of relatively smallforces whose magnitude varies within a narrow range.

A further object of the invention is to provide a friction clutch whichcan be disengaged in response to the application of relatively small andrelatively constant forces at least during a major part of disengagementof the pressure plates from the clutch disc.

An additional object of the invention is to provide a friction clutchwhich is constructed and assembled in such a way that it can bedisengaged in response to the application of relatively smalldisengaging forces the magnitude of which varies within a narrow rangeand without abrupt peaks or valleys.

Still another object of the invention is to provide a clutch which canbe disengaged by forces the difference between the maximum and minimumvalues of which is much smaller than in heretofore known clutches andneed not exceed (and can be even less than) 1.5.

A further object of the invention is to provide a novel and improvedfriction clutch which exhibits the above outlined desirablecharacteristics and which need not be bulkier, heavier and/or moreexpensive than heretofore known friction clutches.

Another object of the invention is to provide a novel and improvedcombination of energy storing elements for use in the above outlinedfriction clutch.

An additional object of the invention is to provide a novel and improvedcombination of cooperating diaphragm springs for use in the aboveoutlined friction clutch.

Still another object of the invention is to provide a power train,particularly for use in motor vehicles, which embodies a friction clutchof the above outlined character.

A further object of the invention is to provide a novel and improvedcombination of components, including means for compensating for wearupon the friction linings and/or pressure plates and/or other elements,for use in the above outlined friction clutch.

Another object of the invention is to provide a novel and improvedcombination of energy storing elements which exhibit superiorforce-to-distance characteristics during engagement as well as duringdisengagement of the above outlined friction clutch.

An additional object of the invention is to provide a novel and improvedmethod of reducing the magnitude and/or the fluctuations of forces whichare necessary to disengage the above outlined friction clutch.

Still another object of the invention is to provide a friction clutchwhich can be utilized in presently known motor vehicles and for otherpurposes as a superior substitute for heretofore known frictionclutches.

SUMMARY OF THE INVENTION

One feature of the present invention resides in the provision of anengageable and disengageable friction clutch which can be utilized withparticular advantage in the power trains of motor vehicles and comprisesa housing or cover adapted to rotate about a predetermined axis, meansfor rotating the housing including a counterpressure plate (e.g., aflywheel receiving torque from the camshaft or crankshaft or anotherrotary output element of a prime mover, such as the combustion engine ofa motor vehicle) which is rotatable about the aforementioned axis, and apressure plate which is coaxial and rotatable with and is disposedbetween the housing and the counterpressure plate and is movable in thedirection of the aforementioned common axis. The friction clutch furthercomprises a clutch disc which is coaxial with and is disposed betweenthe pressure plate and the counterpressure plate and is normallyprovided with friction linings subject to wear upon repeated progressingfrictional contact with and repeated progressing reduction of frictionalcontact with the respective plates in response to axial movement of thepressure plate toward and away from the counterpressure plate, and meansfor engaging the clutch including at least one clutch spring serving tobias the pressure plate against the clutch disc in the engaged conditionof the clutch. The improved friction clutch still further comprisesmeans (e.g., prongs provided on the at least one clutch spring and abearing which can be moved to change the orientation and hence the biasof the at least one clutch spring) for reducing the bias of the at leastone clutch spring upon the pressure plate to thus disengage the clutch,at least one at least temporarily stressed energy storing element whichoperates in parallel with the at least one clutch spring to generateforces promoting (at least in part) the disengagement of the clutch, andmeans for preferably automatically compensating for wear at least uponthe clutch disc, i.e., at least for wear upon the friction linings ofthe clutch disc.

The pressure plate is installed for limited axial movement between thehousing and the counterpressure plate.

The at least one energy storing element can be constructed and installedto exhibit a progressive (rising or growing) force-to-distancecharacteristic, at least during a portion or stage of movement of thepressure plate in a direction to disengage the friction clutch.

The at least one energy storing element and/or the at least one clutchspring can include a diaphragm spring.

If the at least one clutch spring is or includes a diaphragm spring,such diaphragm spring is preferably designed to include an annularportion (such annular portion bears upon the pressure plate at least inthe engaged condition of the clutch) and prongs which extend from theannular portion substantially toward the common axis of the housing andpressure plates (i.e., at least substantially radially of the annularportion) and can form part of the means for reducing the bias of the atleast one clutch spring upon the pressure plate.

The at least one clutch spring can be designed and mounted to have adegressive force-to-distance characteristic, at least during at leastone portion or stage of movement of the pressure plate away from thecounterpressure plate.

The pressure plate covers a predetermined distance during movement awayfrom the counterpressure plate to disengage the clutch. The mounting ofthe pressure plate can be such that the pressure plate applies to theclutch disc a decreasing force during movement of the pressure platethrough a first portion of the predetermined distance and that theclutch disc is spaced apart from (i.e., its friction linings are not infrictional contact with) the pressure plates during movement of thepressure plate through a second portion of the predetermined distance.The arrangement can be such that the at least one energy storing elementexhibits a positive force-to-distance characteristic during movement ofthe pressure plate through the first portion of the predetermineddistance. The at least one energy storing element can be used togenerate forces which promote the disengagement of the clutch duringmovement of the pressure plate through the entire first portion of thepredetermined distance and/or during a part of movement of the pressureplate through the second portion of the predetermined distance.

The at least one energy storing element can bear (directly orindirectly) against the housing or against the bias reducing means andthen reacts (directly or indirectly) against the bias reducing means oragainst the housing. For example, the at least one energy storingelement can bear (directly or indirectly) against the housing or againstthe at least one clutch spring and then reacts (directly or indirectly)against the at least one clutch spring or against the housing.

The at least one energy storing element can be stressed in the engagedcondition of the clutch in such a way that it does not exert any forceor any appreciable force in the direction of the common axis of thepressure plate and the counterpressure plate. Alternatively, the atleast one energy storing element can be installed to exert a relativelysmall force in the direction of the common axis when the clutch isengaged.

It is often desirable to select the at least one energy storing elementin such a way that it exhibits a substantially sinusoidalforce-to-distance characteristic curve and is subjected to a minimumstress (or to a stress not appreciably above the minimum stress) in theengaged condition of the clutch.

It is also possible to select and install the at least one energystoring element in such a way that it is stressed in the engagedcondition of the clutch to generate a force acting in the direction ofthe common axis of the pressure plate and the counterpressure plate.

The clutch disc can further comprise resilient means installed betweenthe friction linings and serving to urge the friction linings in thedirection of the aforementioned axis and away from each other (i.e., tourge one friction lining or one set of friction linings toward thepressure plate and to urge the other friction lining or the other set offriction linings toward the counterpressure plate). Such resilient meansrender it possible to achieve gradual engagement and disengagement ofthe friction clutch.

If the at least one energy storing element comprises or constitutes adiaphragm spring, the friction clutch can further comprise means fortiltably mounting the diaphragm spring on the housing. The arrangementcan be such that the means for tiltably mounting is designed toarticulately connect the housing with a radially outer portion of thediaphragm spring.

Furthermore, and if the at least one energy storing element includes orconstitutes a diaphragm spring, a radially inner portion of suchdiaphragm spring can act upon the bias reducing means of the improvedclutch.

Another feature of the invention resides in the provision of anengageable and disengageable friction clutch which can be utilized withparticular advantage in the power trains between the prime movers andthe wheels of motor vehicles. The clutch comprises a housing which isrotatable about a predetermined axis, means for rotating the housingincluding a counterpressure plate (such as a flywheel adapted to receivetorque from the output element of a combustion engine in a motorvehicle) which is rotatable about the predetermined axis, and a pressureplate which is coaxial with and is rotatable with and is disposedbetween the housing and the counterpressure plate and is movable withinlimits in the direction of the common axis of the housing andcounterpressure plate. The friction clutch further comprises a clutchdisc which is coaxial with and is disposed between the pressure plateand the counterpressure plate and has friction linings subject to wearupon repeated progressing frictional contact and repreated progressingreduction of frictional contact with the pressure plate and thecounterpressure plate in response to axial movement of the pressureplate toward and away from the counterpressure plate, means for movingthe pressure plate including at least one first diaphragm spring servingto bias the pressure plate against the clutch disc in the engagedcondition of the clutch, means for reducing the bias of the at least onefirst diaphragm spring upon the pressure plate to thus disengage theclutch, at least one stressed second diaphragm spring which is operativein parallel with the at least one first diaphragm spring to generateforces promoting at least in part the disengagement of the clutch, andmeans for automatically compensating for wear at least upon the frictionlinings. The wear compensating means includes means for adjusting thebias of the at least one first diaphragm spring upon the pressure plate.

The at least one second diaphragm spring is or can be constructed andarranged to exhibit a progressive force-to-distance characteristic atleast during at least one portion or stage of movement of the pressureplate in a direction to disengage the clutch.

The at least one first diaphragm spring can include an annular portionand projections (e.g., in the form of prongs) extending from the annularportion substantially toward the axis (i.e., radially inwardly of theannular portion) and forming part of the means for reducing the bias ofthe at least one first diaphragm spring (clutch spring) upon thepressure plate.

The at least one first diaphragm spring can have a degressiveforce-to-distance characteristic, at least during at least one portionor stage of movement of the pressure plate away from the counterpressureplate.

The pressure plate covers a predetermined distance during movement awayfrom the counterpressure plate to disengage the clutch. The arrangementis or can be such that the pressure plate applies to the clutch disc adecreasing force during movement through a first portion of thepredetermined distance in a direction away from the counterpressureplate, and that the clutch disc is spaced apart from the pressure plateand the counterpressure plate during movement of the pressure platethrough a second portion of the predetermined distance on its way awayfrom the counterpressure plate. The at least one second diaphragm springwhich is put to use in such friction clutch can be designed to exhibit apositive force-to-distance characteristic during movement of thepressure plate through the first portion of the predetermined distance.Such at least one second diaphragm spring can be installed to generateforces which promote the disengagement of the clutch during movement ofthe pressure plate through the entire first portion of the predetermineddistance. It is further possible to select and install the at least onesecond diaphragm spring in such a way that it is operative to generateforces tending to promote the disengagement of the clutch during a partof movement of the pressure plate through the second portion of thepredetermined distance.

The at least one second diaphragm spring can bear, directly orindirectly, against the housing or against the bias reducing means andthen reacts (directly or indirectly) against the bias reducing means oragainst the housing. For example, the at least one second diaphragmspring can bear (directly or indirectly) against the housing or againstthe at least one first diaphragm spring and then reacts (directly orindirectly) against the at least one first diaphragm spring or againstthe housing.

The at least one second diaphragm spring can be installed in such a waythat it is stressed in the engaged condition of the clutch but does notexert any force (or does not exert any appreciable force) in thedirection of the common axis of the pressure plate and thecounterpressure plate. Alternatively, when stressed in the engagedcondition of the clutch, the at least one second diaphragm spring canexert a relatively small force in the the direction of the common axis.

The at least one second diaphragm spring can have a substantiallysinusoidal force-to-distance characteristic curve and is or can beinstalled in such a way that it is subjected to a minimum stress (or toa stress at least very close to the minimum stress) in the engagedcondition of the clutch.

As already mentioned above, the at least one second diaphragm spring canbe stressed in the engaged condition of the clutch to generate a forcein the direction of the common axis of the pressure plate and thecounterpressure plate.

The clutch disc can further comprise the aforementioned resilient means,e.g., one or more leaf springs or other suitable springs which aredisposed between the friction linings and urge the friction linings forthe pressure plate and the counterpressure plate away from each other inthe direction of the common axis of the pressure plate and thecounterpressure plate.

The friction clutch can further comprise means for tiltably mounting theat least one second diaphragm spring on the housing. The arrangement canbe such that a radially outer portion of the at least one seconddiaphragm spring is tiltably mounted on (i.e., articulately connectedwith) the housing. A radially inner portion of the at least one seconddiaphragm spring can act upon the bias reducing means.

A further feature of the invention resides in the provision of anengageable and disengageable friction clutch which can be utilized withadvantage in motor vehicles to transmit or to interrupt the transmissionof torque between a prime mover (such as a combustion engine) and atransmission or another torque receiving device. The friction clutchcomprises a housing which is rotatable about a predetermined axis, meansfor rotating the housing including a counterpressure plate (such as aflywheel) which is rotatable about the predetermined axis and can befixedly secured to the housing, and a pressure plate which is coaxialand rotatable with and is disposed between the housing and thecounterpressure plate for limited movement in the direction of thecommon axis of the housing and the counterpressure plate. The frictionclutch also comprises a clutch disc which is coaxial with and isdisposed between the pressure plate and the counterpressure plate andhas friction linings which are subject to wear upon repeated progressivefrictional contact and repeated progressing reduction of frictionalcontact with the pressure plate and the counterpressure plate inresponse to axial movement of the pressure plate toward and away fromthe counterpressure plate, means for moving the pressure plate includingat least one first energy storing element arranged to bias the pressureplate against the clutch disc in the engaged condition of the clutch,means for reducing the bias of the at least one first energy storingelement upon the pressure plate to thus disengage the clutch, at leastone second energy storing element which operates in parallel with the atleast one first energy storing element to generate forces which promotethe disengagement of the clutch, resilient means disposed between thefriction linings of the clutch disc and also serving to generate forceswhich promote the disengagement of the clutch, and means for preferablyautomatically compensating for wear at least upon the friction linings.If desired, such compensating means can be designed to change thepositions of the pressure plate and the at least one first energystoring element relative to each other to an extent which is necessaryto compensate for wear upon the friction linings and also for wear uponthe pressure plate, the counterpressure plate, the at least one firstenergy storing element and/or the housing during the useful life of thefriction clutch.

The at least one second energy storing element can be constructed andinstalled to exhibit a progressive force-to-distance characteristic atleast during at least one portion or stage of movement of the pressureplate in a direction to disengage the clutch.

The at least one first energy storing element and/or the at least onesecond energy storing element can include or constitute a diaphragmspring.

The at least one first energy storing element can include or constitutea spring (e.g., a diaphragm spring) having an annular portion (which canbias the pressure plate in the engaged condition of the clutch) andprongs or analogous or similar projections or protuberances extendingfrom the annular portion substantially or exactly toward the common axisof the pressure plate and the counterpressure plate and forming part ofthe means for reducing the bias of the at least one first energy storingelement upon the pressure plate.

The at least one first energy storing element can be constructed andinstalled to exhibit a degressive force-to-distance characteristic atleast during at least one portion or stage of movement of the pressureplate in a direction away from the counterpressure plate.

The pressure plate covers a predetermined distance during axial movementaway from the counterpressure plate in order to disengage the clutch.The friction clutch is preferably designed and assembled in such a waythat the pressure plate applies to the clutch disc a decreasing forceduring movement through a first or initial portion of the predetermineddistance, and the clutch disc is or can be spaced apart from thepressure plate and/or from the counterpressure plate during movement ofthe pressure plate through a second or next-following portion of thepredetermined distance. The at least one second energy storing elementcan exhibit a positive force-to-distance characteristic during movementof the pressure plate through the first or initial portion of thepredetermined distance. The arrangement can be such that the at leastone second energy storing element generates forces which promote thedisengagement of the clutch during movement of the pressure platethrough the entire first or initial portion of the predetermineddistance. Furthermore, the clutch can be constructed and assembled insuch a way that the at least one second energy storing element isoperative to generate forces which tend to promote the disengagement ofthe clutch at least during a part of movement of the pressure platethrough the second or next-following portion of the predetermineddistance.

The at least one second energy storing element can bear (directly orindirectly) against the housing or against the bias reducing means andthen reacts (either directly or indirectly) against the bias reducingmeans or against the housing. For example, the at least one secondenergy storing element can bear (directly or indirectly) against thehousing or against the at least one first energy storing element andthen reacts against the at least one first energy storing element oragainst the housing.

The at least one second energy storing element can be stressed, in theengaged condition of the clutch, in such a way that it does not exertany (or does not exert any appreciable or noticeable) force in thedirection of the common axis of the pressure plate and thecounterpressure plate. Alternatively, the at least one second energystoring element can be stressed (in the engaged condition of the clutch)in such a way that it exerts a relatively small force in the directionof the common axis of the pressure plate and the counterpressure plate.

It is often preferred to select an at least one second energy storingelement having a substantially sinusoidal force-to-distancecharacteristic curve and being subjected to a minimal stress (or to astress at least very close to the minimal stress) in the engagedcondition of the friction clutch.

As already mentioned above, the at least one second energy storingelement can be stressed when the friction clutch is engaged, and suchstressed element can be installed and designed not to generate anyappreciable forces in the direction of the common axis of the pressureplate and the counterpressure plate or to generate a relatively smallforce in the direction of such axis. However, it is also within thepurview of the invention to employ one or more second energy storingelements capable of generating pronounced or relatively large forces inthe direction of the common axis of the pressure plate and thecounterpressure plate when the clutch is engaged.

The aforementioned resilient means of the clutch disc can include atleast one spring (e.g., a leaf spring) which biases the friction liningsaway from each other in the direction of the common axis of the pressureplate and the counterpressure plate. Such spring or springs ensuresmooth or gradual engagement as well as smooth or gradual disengagementof the friction clutch because they can gradually yield duringengagement of the clutch (when the pressure plate is caused to movetoward the counterpressure plate) and because they can graduallydissipate energy during movement of the pressure plate away from thecounterpressure plate.

If the at least one second energy storing element includes orconstitutes a diaphragm spring, the friction clutch can further comprisemeans for tiltably mounting the diaphragm spring on the housing. Thetiltable mounting can involve the establishment of an articulateconnection between a radially outer portion of the diaphragm spring ofthe at least one second energy storing element and the housing. Aradially inner portion of a diaphragm spring forming part of orconstituting the at least one second energy storing element can bemounted to act upon the bias reducing means of the friction clutch.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved friction clutch itself, however, both as to its constructionand the mode of assembling and using the same, together with additionalfeatures and advantages thereof, will be best understood upon perusal ofthe following detailed description of certain presently preferredspecific embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary axial sectional view of a friction clutch whichembodies one form of the invention;

FIG. 2 is a fragmentary sectional view substantially as seen in thedirection of arrows from the line II--II in FIG. 1;

FIG. 3 is a diagram showing the relationship of forces generated andapplied by various constituents of the friction clutch of FIGS. 1 and 2;

FIG. 4 is another diagram;

FIG. 5 is a fragmentary axial sectional view of a modified frictionclutch;

FIG. 6 is a plan view of a detail in the friction clutch of FIG. 5;

FIG. 7 is a fragmentary axial sectional view of a third friction clutch;

FIG. 8 is a plan view of a detail in the friction clutch of FIG. 7; and

FIG. 9 is an axial sectional view of still another friction clutch whichembodies the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 2 illustrate certain details of a so-called pull typefriction clutch 1 which comprises a housing or cover 2 rotatable aboutan axis corresponding to the axis X--X shown in FIG. 9, and serving totransmit torque to a pressure plate 3. The means for transmitting torquefrom the housing 2 to the pressure plate 3 can comprise suitable leafsprings (shown in FIG. 9, as at 209) which enable the pressure plate toperform limited movements in the direction of the common axis of theparts 2, 3 but compel the pressure plate to share all angular movementsof the housing.

When the clutch 1 is engaged, a clutch spring 4 (here shown as adiaphragm spring) biases the pressure plate 3 against the adjacentfriction lining or linings 7 of a clutch disc 8 which is interposedbetween the pressure plate and a counterpressure plate 6. The housing 2carries a ring-shaped seat assembly 5 which tiltably supports thecircumferentially complete annular radially outer or main portion 4a ofthe clutch spring 4. The counterpressure plate 6 is coaxial with and isrigidly connected to the marginal portion of the housing 2 and serves asa means for rotating the housing 2 and hence also the pressure plate 3,the clutch disc 8 (when the clutch 1 is engaged) and the clutch spring4. The counterpressure plate 6 can constitute a flywheel (or can formpart of a composite flywheel) which is affixed to a rotary outputelement (such as a camshaft or a crankshaft) of a prime mover, e.g., acombustion engine in a motor vehicle. The hub (not shown in FIGS. 1 and2) of the clutch disc or clutch plate 8 can transmit torque to the inputshaft of a transmission in the power train between the engine and thewheels of the vehicle. Reference may be had, for example, to commonlyowned U.S. Pat. No. 5,180,335 granted Jan. 19, 1993 to Paul Maucher for"Torsion damping assembly for use with clutches in motor vehicles". Thedisclosure of this patent is incorporated herein by reference.

The clutch disc 8 comprises two friction linings or two sets of frictionlinings 7 and one or more energy storing resilient segments 10 betweenthe friction linings. When the clutch 1 is in use, the friction linings7 undergo wear as a result of repeated progressing frictional contactwith the plates 3, 6 during engagement of the clutch as well as due torepeated progressing reduction of frictional contact with the adjacentplates during disengagement of the clutch. The resilient segments 10serve as a means for ensuring gradual engagement of the clutch 1 inresponse to axial movement of the pressure plate 3 toward thecounterpressure plate 6 (the segments then yield to permit gradualmovement of the two friction linings 7 toward each other), and thesegments 10 also ensure gradual or smooth disengagement of the clutchbecause they move the friction linings 7 apart during the initial stageof disegagement, i.e., when the pressure plate 3 begins to move axiallyand away from the counterpressure plate 6. Otherwise stated, theresilient segments ensure a gradual rise of axial forces acting upon thelinings 7 in the course of engagement of the clutch 1 (namely duringmovement of the pressure plate 3 toward the counterpressure plate 6) anda gradual reduction of such axial forces at least during the initialstage of disengagement of the clutch (namely when the pressure plate 3begins to move axially and away from the counterpressure plate 6). Theclutch disc or clutch plate 8 is preferably constructed and assembled insuch a way that the friction linings 7 have limited freedom of axialmovement away from each other under the bias of the resilient segments10.

The illustrated clutch spring (diaphragm spring) 4 includes a set ofresilient prongs 4b or analogous projections or protuberances whichextend from the radially outer portion 4a toward the common axis of theparts 2, 3, 4, 5, 6 and 8, i.e., radially inwardly from the portion 4a.When the clutch 1 is engaged, the radially outer portion 4a of theclutch spring 4 urges the pressure plate 3 against the adjacent frictionlining 7 and the prongs 4b are unstressed or are not stressedsufficiently to compel the spring 4 to pivot at 5 relative to thehousing 2 to an extent which is needed to effect a disengagement of theclutch 1 by enabling the aforementioned leaf springs to move thepressure plate 3 axially and away from the counterpressure plate 6.

The seat assembly 5 of the friction clutch 1 which is shown in FIGS. 1and 2 is located radially outwardly of the location where the springportion 4a acts upon the pressure plate 3 when the clutch is engaged.This assembly includes an annular seat 11 (e.g., a wire ring) which isinterposed between the bottom wall of the housing 2 and the radiallyoutermost part of the circumferentially complete portion 4a of theclutch spring 4. The seat 11 is centered in the adjacent portion of thesubstantially radially extending bottom wall of the housing 2 so thatits axis coincides with the common axis of the housing 2, pressure plate3 and the aforementioned several other parts of the friction clutch 1.The housing 2 and/or the clutch spring 4 further comprises means forpreventing rotation of these parts relative to each other, i.e., theclutch spring shares all angular movements of the plates 3 and 6.

The friction clutch 1 further comprises means (denoted by the character12) for automatically compensating for wear at least upon the frictionlinings 7 of the clutch plate or disc 8. It is preferred to design thecompensating means 12 in such a way that, in addition to the wear uponthe friction linings 7, it can also compensate for wear upon one or moreadditional constituents of the friction clutch 1, such as the pressureplate 3, the counterpressure plate 6, the clutch spring 4 and/or thehousing 2.

The illustrated wear compensating means 12 comprises a wear compensatingunit proper (shown at 13) which is interposed between the clutch spring4 and the pressure plate 3, and a sensor 14 which serves as a means formonitoring or detecting the extent of wear at least upon the frictionlinings 7. The sensor 14 and the wear compensating unit 13 are disposedat the same radial distance (or at least close to the same radialdistance) from the common axis of the housing 2 and pressure plate 3.Furthermore, the sensor 14 overlies the wear compensating unit 13, asseen in the axial direction of the friction clutch 1 from the housing 2toward the pressure plate 3.

The sensor 14 is a composite monitoring device including an annulararray of preferably equidistant discrete sensor elements 15. Each sensorelement 15 comprises a sleeve-like member 16 which is movable inparallelism with the axis of the housing 2 along one of several axiallyparallel protuberances or studs 17 anchored in the pressure plate 3 andextending through and beyond the bottom wall of the housing 2. Theillustrated stud 17 is a separately produced part which is anchored inthe pressure plate 3; however, it is equally possible to make the studs17 of one piece with the pressure plate.

The internal surface of each sleeve-like member 16 is in frictionalengagement with the peripheral surface of the respective stud 17. Forexample, each member 16 can be provided with axially parallel slitswhich alternate with axially parallel tongues or prongs tending to pivotradially inwardly toward frictional engagement with the peripheralsurface of the corresponding stud 17. Thus, the inner diameter of thatpart of a sleeve-like member 16 which is provided with theaforementioned tongues or prongs is less than the diameter of a stud 17when the member 16 is slipped off such stud.

The axially outer end portion of each sleeve-like member 16 includes aradially outwardly extending collar 19 constituting a stop which canmove into abutment with the external surface of the bottom wall of thehousing 2. The collar 19 can move into actual contact with the housing 2at least after the friction linings 7 have already undergone a certainamount of wear as a result of repeated progressing frictional contactand repeated reduction of frictional contact with the adjacent plates 3and 6. The radially outer portion 4a of the clutch spring 4 is providedwith openings for the studs 17 and the sleeve-like members 16 of therespective sensor elements 15.

When the clutch 1 is engaged after the friction linings 7 have alreadyundergone a certain amount of wear, the collars 19 move into engagementwith the housing 2 in response to engagement of the clutch 1, and thisensures that the axial position of the pressure plate 3 relative to thesleeve-like members 16 is changed through a distance corresponding tothe extent of wear upon the friction linings.

The wear compensating unit 13 of the wear compensating means 12comprises a ring-shaped compensating element 20 which can be made ofmetallic sheet material and has a substantially U-shaped cross-sectionaloutline. When the clutch 1 is engaged, the ring-shaped element 20 isacted upon by the clutch spring 4 so that it causes the pressure plate 3to bear against the adjacent friction lining 7 of the clutch disc 8. Inother words, the ring-shaped element 20 serves as a means fortransmitting axially oriented forces from the clutch spring 4 to thepressure plate 3.

The wear compensating unit 13 further comprises an adjusting device 21which is installed between the ring-shaped element 20 and the pressureplate 3 and renders it possible to achieve an automatic shifting(adjustement) of the ring-shaped element 20, in response todisengagement of the clutch 1, when necessary to compensate for initialor additional wear upon the friction linings 7. On the other hand, theadjusting device 21 is self-locking when the clutch 1 is engaged, i.e.,the ring-shaped element 20 can change its axial position relative to thepressure plate 3 only when the clutch is disengaged. This is desirableand advantageous because the axial position of the ring-shaped element20 relative to the pressure plate 3 is fixed during axial movement ofthe pressure plate 3 toward the counterpressure plate 6, i.e., in adirection to clamp the friction linings 7 between the adjacent frictionfaces of the respective plates 3 and 6. The ability of the wearcompensating unit 13 to prevent any attempts at compensation for wearduring movement of the pressure plate 3 in a direction to engage theclutch 1 and/or during actual engagement of the clutch constitutes adesirable safety feature which contributes to more predictable and moreaccurate compensation for wear upon the friction linings 7 and, ifdesired or necessary, upon one or more additional parts which aresubject to wear or are likely to be subjected to wear in actual use ofthe friction clutch.

The adjusting device 21 which is shown in FIGS. 1 and 2 comprises anarray of pairs of circumferentially extending ramps 22, 23. The ramps ofeach pair have abutting surfaces which slope axially as well ascircumferentially of the pressure plate 3. The ramps 22 are shown asintegral parts of (actually of one piece with) the ring-shaped 5 element20, and the ramps 23 are integral (and can be of one piece) with thepressure plate. The ring-shaped element 20 has a relatively shortcylindrical radially outer portion 24 whose axis coincides with the axisof the pressure plate 3 and which is provided with suitable triangularcutouts to thus form the ramps 22. The ramps 23 can constitute suitablyconfigurated projections at that side of the pressure plate 3 whichconfronts the inner side of the bottom wall of the housing 2.

The ramps 22 of the adjusting device 21 which is shown in FIGS. 1 and 2directly abut the adjacent ramps 23, and the abutting sloping surfacesof the pairs of cooperating ramps are biased against each other. This isachieved by the provision of energy storing elements 25 here shown ascoil springs which act in the circumferential direction of the pressureplate 3. Each coil spring 25 reacts against the pressure plate 3 oragainst the ring-shaped element 20 and bears against the element 20 oragainst the presure plate.

The ring-shaped element 20 can turn relative to the pressure plate 3,and this involves a sliding movement of the ramps 22 along the adjacentramps 23. Such turning of the element 20 relative to the pressure plate3 is made possible by the provision of suitable windows or slots 26formed in the element 20 and dimensioned to receive the studs 17 of thepressure plate 3 with requisite clearance which is required to permitsufficient angular displacements of the element 20 relative to thepressure plate to compensate for wear upon the friction linings 7 duringthe entire useful life of the clutch disc 8 (preferably during theentire useful life of the friction clutch 1).

The angle 27 (shown in FIG. 2) of slope of the abutting surfaces of theramps 22, 23 (relative to a plane which is normal to the axis of thepressure plate 3) is selected in such a way that, when the ramps 22 areurged against the adjacent ramps 23, the frictional engagement betweenthe abutting surfaces of such pairs of ramps suffices to prevent any orany appreciable angular displacements of the ring-shaped element 20relative to the pressure plate 3. The exact magnitude of the angle 27will depend upon a plurality of factors, e.g., the material of the ramps22, 23, the finish of the abutting surfaces of the pairs of ramps andthe bias of the clutch spring 4. It is presently preferred to select anangle 27 within the range of between about 4° and 15°, most preferablybetween about 4° and about 8°.

The direction in which the ring-shaped element 20 must turn relative tothe pressure plate 3 in order to compensate for wear upon the frictionlinings 7 is indicated in FIG. 2 by an arrow 28. It will be noted thatthe apices of the angles 27 of slope of the ramps 22 forming part of thering-shaped element 20 face in the direction of the arrow 28.

The bias of the coil springs 25 (i.e., the force with which the ramps 22bear against the adjacent ramps 23) and the magnitude of the angle 27 ofslope of the abutting surfaces of the ramps 22, 23 are selected in sucha way that the resultant axial force acting upon the ring-shaped element20 is much smaller than the force which is required to move thesleeve-like elements 16 of the sensors 15 in the axial direction of therespective studs 17.

If the friction clutch 1 is not provided with any axially fixed stop orstops which would limit the extent of axial movability of the pressureplate 3 relative to an axially fixed part (such as the housing 2 or thecounterpressure plate 6), the aforementioned resultant axial forceacting upon the ring-shaped element 20 is selected (with reference tothe axial force exerted by the leaf springs (corresponding to the leafsprings 209 shown in FIG. 9) which bias the pressure plate 3 axially andaway from the counterpressure plate 6) in such a way that the wearcompensating unit 13 is capable of performing its intended function. Itis presently considered advisable to select the stress of the leafsprings (209) in such a way that the axial force exerted thereby uponthe pressure plate 3 in the disengaged condition of the clutch 1 is nilor close to nil. At any rate, the axial force then exerted by the leafsprings is less than the axial force acting upon the ring-shaped element20.

It is often preferred to provide one or more abutments or stops (oneshown in FIG. 1, as at 29) which limit the extent of axial movability ofthe pressure plate 3 in a direction away from the counterpressure plate6, i.e., toward the bottom wall of the housing 2. Such stop or stops 29ensure that the extent of axial movement of the pressure plate 3 for thepurpose of effecting disengagement of the clutch 1 is always the same.The illustrated stop 29 changes its axial position as a function of theextent of progressing wear upon the friction linings 7.

The construction of the wear compensating means 12 can be simplified ifit embodies or includes the stop or stops 29. The stop 29 which is shownin FIG. 1 is an integral part of the sleeve-like member 16 of therespective sensor element 15. This stop strikes against and is arrestedby the inner side of the bottom wall of the housing 3 when the pressureplate 3 completes a movement through a predetermined distance axiallyand away from the counterpressure plate 6. For example, the distance 30to be covered by the pressure plate 3 during disengagement of the clutch1 can be in the range of between about 1.5 mm and 3 mm. The illustratedstop 29 of the sleeve-like member 16 then strikes the surfacesurrounding the inner end of the opening provided in the bottom wall ofthe housing 2 for the respective stud 17 and member 16. Theaforementioned distance range of between about 1.5 mm and about 3 mm canbe exceeded or shortened in dependency on the exact nature of thefriction clutch and its wear compensating means. Furthermore, the stopor stops 29 need not form part of the wear compensating means 12, i.e.,such stop or stops can constitute separately produced and mounted parts.Attention is invited, for example, to U.S. Pat. No. 4,207,972 thedisclosure of which is incorporated herein by reference.

In selecting the characteristics oft he clutch spring 4, it is necessaryto take into consideration that this spring must overcome the bias ofthe leaf springs (209) during engagement of the clutch 1 as well as thatthe spring 4 should be capable of shifting the sleeve-like member 16along the respective studs 17. As concerns the exact nature of leafsprings which can be utilized in the friction clutch 1 of FIGS. 1 and 2to bias the pressure plate 3 axially and away from the counterpressureplate, the inventor invites attention to U.S. Pat. No. 4,615,424 thedisclosure of which is incorporated herein by reference.

The leaf springs (209) not only bias the pressure plate 3 axially andaway from the counterpressure plate 6 but they also serve to transmittorque from the housing 2 to the pressure plate. Their stressing in theengaged condition of the clutch 1 is or should be sufficient to ensurethat the pressure plate 3 is actually moved axially and away from thecounterpressure plate 6 during disengagement of the clutch which takesplace as a result of a reduction of the bias of the clutch spring 4 uponthe pressure plate. Such selection of the bias of the leaf springs uponthe pressure plate 3 ensures that the ring-shaped element 20 continuesto contact the clutch spring 4 during the entire clutch disengagingoperation. If the clutch is provided with one or more stops 29, theelement 20 continues to bear against the clutch spring 4 until the stopor stops 29 reach the inner side of the bottom wall of the housing 2.

FIG. 1 shows that the illustrated wear compensating means 12 isdesigned, assembled and mounted in such a way that the regions ofcontact between the ramps 22 and the neighboring ramps 23, the annularregion of contact between the ring-shaped element 20 and the clutchspring 4, and the annulus of regions of contact between the ring-shapedelement 20 and the sleeve-like member 16 are disposed at the same (or atleast close to the same) radial distance from the common axis of thehousing 2 and pressure plate. In other words, the aforementioned regionsoverlie each other as seen in the axial direction of the housing 2 andpressure plate 3. In the wear compensating means 12 of FIGS. 1 and 2,the collars 19 and the stops 29 are also disposed at or close to thesame radial distance 38 from the axis of the housing 2 as the ring 20and the ramps 22, 23.

If the clutch 1 is provided with one or more stops 29 to limit theextent of axial movability of the pressure plate 3 away from thecounterpressure plate 6, the path for disengagement in the region of theradially inner end portions or tips 4c of the prongs 4b forming part ofthe clutch spring 4 is or can be selected in such a way that, when theclutch is disengaged, the clutch spring 4 is slightly spaced apart fromthe ring-shaped element 20 in the axial direction of the housing 2.Thus, the axial distance covered by the clutch spring 4 at the radialdistance 38 of the ring-shaped element 20 from the axis of the housing 2exceeds the maximum distance which can be covered by the pressure plate3 away from the counterpressure plate 6 due to the provision of thestop(s) 29.

In accordance with a feature of the invention, the clutch 1 furthercomprises an energy storing element 31 which operates in parallel withthe clutch spring 4 and serves to generate forces which promote, atleast in part, the disengagement of the clutch. The illustrated energystoring element 31 is a diaphragm spring which has a circumferentiallycomplete annular radially outer portion 32 tiltably coupled to thehousing 2 and radially inwardly extending tongues, prongs or likeprotuberances 33 which are coupled to the prongs 4b of the clutch spring4. As can be seen in FIG. 1, the energy storing element 31 is installedat the outer side of the bottom wall of the housing 2. The means forcoupling the tongues 33 of the energy storing element 31 to the prongs4b of the clutch spring 4 includes rivets 35. The heads 36 of the rivets35 serve as abutments or stops which limit the extent of movability ofthe tips of the tongues 33 axially of the housing 2 and away from theadjacent prongs 4b.

The energy storing element 31 is preferably mounted on the housing 2 inan at least slightly axially stressed condition, most preferably in sucha way that the axial stress upon the element 31 is at or close to apredetermined minimum value. Such minimum value develops when theelement 31 is a diaphragm spring having an at least substantiallysinusoidal force-to-distance characteristic.

When the clutch 1 is engaged, the axial force which the energy storingelement 31 applies to the clutch spring 4 is preferably zero or close tozero. However, it is often preferred and desirable to mount the element31 in such a way that it exerts upon the clutch spring 4 a relativelysmall force in a direction (arrow 37 in FIG. 1) to disengage the clutchwhen the clutch is fully engaged. The element 31 can be said toconstitute a servo whose bias to urge the tips 4c of the prongs 4b inthe direction of arrow 37 increases during disengagement of the clutch.The prongs 4b constitute means for reducing the bias of the clutchspring 4 upon the pressure plate 3 (so that the latter can move awayfrom the counterpressure plate 6 under the action of the leaf springs(209) and the resilient segments 10) during disengagement of the clutch.

The bias of the energy storing element 31 upon the clutch spring 4increases during the initial stage or portion of actual disengagement ofthe clutch 1 to thereupon decrease as the disengagement of the clutchprogresses. Otherwise stated, the element 31 initially exerts upon thespring 4 an increasing force in the direction of the arrow 37, and theforce which the element 31 exerts in such direction thereupon decreases.That stage when the element 31 exerts a maximum force in the directionof the arrow 37 (i.e., when such force begins to decrease as thedisengagement of the clutch progresses) is reached when the curvedenoting the progress of the disengaging forces reaches or is at leastclose to a lowermost point. The stressing of the element 31 can decreaseto zero prior to completion of the disengaging operation. As thedisengagement continues (i.e., as the tips 4c of the prongs 4b continueto move in the direction of the arrow 37), only the conicity of theclutch spring 4 (which, in the embodiment of FIGS. 1 and 2, is adiaphragm spring) is caused to change because the spring 4 is caused topivot at the locus defined by the seat assembly 5. This means that, asthe disengagement of the clutch 1 progresses subsequent to unstressingof the energy storing element 31, the progress of the disengaging forceup to completion of the disengaging operation is determined (eitherprimarily or exclusively) by the clutch spring 4.

The diagrams which are shown in FIGS. 3 and 4 are intended to facilitatethe understanding of the relationships of various forces which developin actual use of a friction clutch of the type shown in FIGS. 1 and 2 inthe power train between the combustion engine and the transmission of amotor vehicle, e.g., a truck.

The sinusoidal curve 40 in the diagram of FIG. 3 denotes the progress ofaxial forces while the conicity of the clutch spring 4 changes and bytaking into consideration certain other influences such as the bias ofleaf springs (209) acting upon the pressure plate 3 in a direction tomove it away from the counterpressure plate 6. It is assumed that theclutch spring 4 has undergone a deformation starting from a fullyunstressed position between two radially spaced apart locations, namelythe radially outer location determined by the position of the seatassembly 5 and the radially inner location (at 38) determined by thediameter of that portion of the ring-shaped element 20 which is incontact with the adjacent side of the spring 4, namely at the radius 38from the axis of the housing 2. The distance covered by the clutchspring 4 between the two (radially inner and radially outer) locations(in millimeters) is measured along the abscissa and the magnitude of theresultant force generated by the spring 4 and the leaf springs (209) ismeasured along the ordinate. The point 41 on the curve 40 denotes themagnitude of the resultant force when the clutch 1 is engaged, i.e.,when the clutch spring 4 is called upon to apply to the pressure plate 3a maximum force in a direction to maintain the clutch in fully engagedcondition. The point 41 can be shifted along the curve 40 in a directiontoward or away from the ordinate of the diagram of FIG. 3 by changingthe conicity of the clutch spring 4 in the engaged condition of theclutch.

The broken-line curve 42 in the diagram of FIG. 3 denotes the axiallyoriented spreading force which is generated by the resilient segments 10between the friction linings 7 of the clutch disc 8. The curve 42 canfurther denote certain other axially oriented forces which act in thesame direction as the forces generated by the resilient segments 10;such other axially oriented forces can be caused, for example, by theresiliency of the cover or housing 2, the resiliency or elasticity (ifany) of the seat assembly 5 and/or the elasticity of resilient inserts(if any) between the clutch spring 4 and the pressure plate 3. The forcedenoted by the curve 42 opposes the force (curve 40) which is generatedby the clutch spring 4 and is being applied to the pressure plate 3.

It has been found that the operation of the clutch 1 is particularlysatisfactory if the magnitude of the axial force necessary to effect amaximum possible elastic deformation of the resilient segments 10between the friction linings 7 of the clutch disc 8 at least matches theaxial force which the clutch spring 4 applies to the pressure plate 3 inthe fully engaged condition of the clutch. The resilient segments 10dissipate energy during disengagement of the clutch, namely while thepressure plate covers a first portion 43 of the maximum possibledistance 50 in a direction axially of and away from the counterpressureplate 6. As already mentioned before, the energy storing element 31operates in parallel with the clutch spring 4 and the element 31 assiststhe bias of the resilient segments 10 during the first stage (distance43 in FIG. 3) of disengagement of the clutch. In other words, themaximum disengaging force can be smaller than that denoted by the point41 on the curve 40, and this is attributable to the provision of aclutch disc which employs resilient segments 10.

When the disengagement of the clutch progresses beyond the point 44(i.e., when the pressure plate 3 continues to move away from thecounterpressure plate 6 beyond the portion 43 of the maximum possibledistance 50), the required disengaging force is much smaller than theSpring force denoted by the point 41 on the curve 40. This isattributable to the degressive characteristic of the curve 40 in theregion of the point 44.

The broken-line curve 45 denotes in the diagram of FIG. 3 the progressof the disengaging force in the absence of the energy storing element31. With reference to the radius 38 (i.e., the locus where the clutchspring 4 acts upon the pressure plate 3), the disengaging force denotedby the curve 45 at first increases to the point 44 to thereupon decreaseat the same rate as the force of the clutch spring 4 (curve 40). Suchdrop of the disengaging force ends at the (lowermost) point 46 of thecurve 40. The force being applied by the clutch spring 4 begins toincrease beyond the point 46 toward the point 47 which is reached whenthe pressure plate 3 has completed its axial movement away from thecounterpressure plate 6.

The curve 40 of FIG. 3, and particularly that part of the curve whichextends between the points 44, 46 and 47, clearly indicates that, in theabsence of the energy storing element 31, the magnitude of thedisengaging force would fluctuate to a considerable extent at least upondisengagement (at 44) of the pressure plate 3 from the adjacent frictionlinings 7 of the clutch disc 8.

The curve 48 in the diagram of FIG. 4 indicates the progress of thedisengaging force at the diameter 4d (FIG. 1) of the friction clutch 1,i.e., of a friction clutch which is equipped with the energy storingelement 31. The diameter 4d is the diameter of the annulus formed by thetips 4c of the prongs 4b forming part of the clutch spring 4. The curve48 corresponds to that portion of the curve 40 in FIG. 3 which includesthe points 44, 46 and 47. The distance which can and should be coveredby the tips 4c in the direction of the arrow 37 under the action of adisengaging bearing 39 or the like is shown in the diagram of FIG. 4, asat 49. This distance exceeds the distance 50 (FIG. 3) by a valuecorresponding to the lever arm of the clutch spring 4. Such lever armcorresponds to the ratio of the radial distance between the seatassembly 5 and half the diameter 4d to the radial distance between theseat assembly 5 and the radius 38 (i.e., the distance of the locus ofcontact between the clutch spring 4 and the ring-shaped element 20 fromthe axis of the pressure plate 3). In many or most instances, the justdefined ratio is between 3:1 and 6:1 but can be more or less, dependingon certain specific circumstances of use of the improved frictionclutch. In the clutch of FIGS. 1 and 2, the ratio is at least close to6:1.

The disengaging force which is indicated by the curve 48 of FIG. 4(while the pressure plate 3 covers the maximum distance 49 duringdisengagement of the clutch 1) is smaller than the force denoted by thecurve 40 of FIG. 3 (at the diameter 4d of the tips 4c of the prongs 4b)by the aforementioned ratio. As already explained before, the curve 45of FIG. 3 denotes the progress of the disengaging force at the radius 38when the clutch does not employ the element 31 or an equivalent of thiselement, such disengaging force being applied while the pressure plate 3covers the first portion 43 of the overall distance 50 which is beingcovered during disengagement of the clutch. The portion 43 is covered bythe pressure plate 3 while it still contacts the adjacent frictionlining 7. The disengaging force denoted by the curve 45 in the diagramof FIG. 3 is the differential between the corresponding portion (betweenthe points 41 and 44) of the disengaging force denoted by the curve 40and the axial spreading force of the resilient segments 10 as denoted bythe curve 42.

The point 44 on the curve 40 of FIG. 3 is reached when the pressureplate 3 completes its movement through the first portion 43 of theoverall distance 50, i.e., when the pressure plate becomes disengagedfrom the adjacent friction linings 7. At such time, the clutch disc 8 isalso disengaged from the counterpressure plate 6. Otherwise stated, thepoint 44 on the curve 40 of FIG. 3 denotes that stage of disengagementof the clutch 1 when the extent of frictional contact between thefriction linings 7 and the plates 3, 6 is zero or at least very close tozero. At such time, the magnitude of the torque being transmitted fromthe plates 3, 6 to the clutch disc 8 is zero or practically nil. Theresilient segments 10 have dissipated their energy.

As the pressure plate 3 continues to move away from the counterpressureplate 6 to cover the second portion 51 of the overall distance 50, theredevelops a progressively increasing clearance or gap between thepressure plate and the clutch disc 8.

The provision of the wear compensating means 12 and of the resilientsegments 10 alone suffices to establish a much more satisfactoryprogress of the disengaging force than in conventional clutches which donot use equivalents of the segments 10 and/or wear compensating means12. However, and as clearly shown by the curve 48 in the diagram of FIG.4, the magnitude of the disengaging force will still fluctuate within arather wide range even if the friction clutch employs the resilientsegments 10 or their equivalents and even if the clutch is equipped withwear compensating means. Thus, and as indicated by that portion of thecurve 48 which denotes the variations of the disengaging force while thetips 4c of the prongs 4b cover the maximum distance 49 duringdisengagement of a clutch employing the resilient segments 10 and thewear compensating means 12 but not the energy storing element 31 of itsequivalent, the difference between the maximum disengaging force (at thepoint 52 of the curve 48) and the minimum disengaging force (at thepoint 53) is still relatively large. The factor denoting the ratio ofdisengaging forces at 52 and 53 is approximately 1.7. In fact, suchfactor will or can exceed (and considerably exceed) 1.7 in many types offriction clutches.

The curve 48 of FIG. 4 indicates that the disengaging force begins torise in response to start of the disengaging operation and reaches thepoint 52 to thereupon decrease to the minimum value at 53. The ratherpronounced difference between the disengaging forces denoted by thepoints 52 and 53 of the curve 48 is or can be undesirable under manycircumstances of the use of the friction clutch. For example, suchrather pronounced difference between the disengaging forces at 52 and 53can interfere with accurate selection of the distance to be covered bythe pressure plate during engagement or disengagement of the clutch.This holds true regardless of whether the clutch is being disengaged bya foot pedal or by a servomotor. For example, if the disengagement is tobe effected by a servomotor (such as an electric motor), the latter mustbe designed to furnish the maximum disengaging force (as denoted by thepoint 53 on the curve 48 in the diagram of FIG. 4). This means that thevehicle must employ a relatively large and bulky servomotor whichconsumes large amounts of energy.

The aforediscussed drawbacks of friction clutches with or withoutresilient segments in their clutch discs and with or without wearcompensating means are overcome by the provision of the energy storingelement 31. The characteristic force-to-distance curve of the element 31is shown in the diagram of FIG. 4, as at 54. In plotting the curve 54,the force which the element 31 applies to the heads 36 of the rivets 35has been replaced by an equivalent force which would act upon the clutchspring 4 at the diameter 4d. Such shifting of the locus of applicationof the force being furnished by the energy storing element 31 has beencarried out by taking into consideration the relevant lever arms.

FIG. 4 shows that the force furnished by the element 31 and acting uponthe clutch disc 4 within the first portion 55 of the overall distancecovered by the the tips 4c of the prongs 4b and the disengaging bearing39 in the direction of arrow 37 (i.e., in a direction to disengage theclutch) increases gradually from a minimum value at 56 to a maximumvalue at 57 to thereupon again decrease to the minimum value (at 58).FIG. 4 further shows that the action of the force denoted by the curve54 is counter to the action of the force denoted by the curve 48. At thepoint 56, the stressing of the energy storing element 31 is or can bezero or close to zero. It is often desirable and advantageous to designand install the element 31 in such a way that, at the point 56, thiselement still applies a residual force (a positive force) in a directionto disengage the clutch, i.e., in a direction as indicated by the arrow37.

The element 31 assists in the disengagement of the clutch while the tips4c and the bearing 39 cover the first portion 55 of the overall distance49 covered by the bearing 39 during disengagement of the clutch. Theforce which is being furnished by the element 31 increases gradually andsubstantially between the points 56 and 57 of the curve 54 to thereupondecrease between the points 57 and 58. The energy storing element 31whose force-to-distance characteristic is denoted by the curve 54 ofFIG. 4 is no longer stressed at the point 58. At such time, the element31 is supported exclusively by the housing 2 of the clutch 1.

It is possible to provide one or more stops which limit the extent ofdissipation of energy by the element 31 during disengagement of theclutch in such a way that the element 31 remains under a residualstress, i.e., that the point 58 of the curve 54 is located at a levelbelow the abscissa in the diagram of FIG. 4. Such stop or stops can beprovided on or can form part of the housing 2. FIG. 1 showsschematically a stop 2a which is provided on or forms part of the bottomwall of the housing 2.

When the movement of the bearing 39 progresses beyond the portion 55 ofthe overall distance 49 which is to be covered during disengagement ofthe clutch 1, the element 31 remains in the fully unstressed condition(or remains under a residual stress as determined by the stop or stops2a) while the clutch spring 4 is free to continue to pivot or be tiltedrelative to the housing 2. This is possible because the rivets 35 aredesigned to establish a predetermined play or clearance 36a betweentheir heads 36 and the adjacent portions of the respective prongs 4b. Inother words, the tongues 33 forming part of the energy storing element31 and the tips 4c of the prongs 4b forming part of the clutch spring 4have a limited freedom of movement relative to each other in thedirection of the axis of the housing 2.

The curve 59 in the diagram of FIG. 4 indicates the resultant ofdisengaging forces denoted by the curves 48 and 54. Such actual orresultant disengaging force is being applied during the initial stage ofmovement of the bearing 39 in the direction of the arrow 37, i.e., inthe direction to disengage the clutch. A curve corresponding to thecurve 59 of FIG. 4 is shown in the diagram of FIG. 3 and is denoted bythe character 60. The curve 60 was plotted by full consideration of theratio of the lever arms at 38 and 4d.

FIG. 4 clearly shows that the provision of the energy storing element 31renders it possible to greatly reduce the difference between the maximumand minimum disengaging forces and that the required maximum disengagingforces are much smaller than in a clutch which does not employ anequivalent of the element 31. It can be said that the element 31 rendersit possible to achieve a linearization or flattening of the curve 59denoting the actual progress of the disengaging force as well as toachieve a substantial reduction of such force. Thus, the maximum 52 ofthe curve 48 is moved a considerable distance toward the abscissa of thediagram of FIG. 4 with resultant pronounced savings in work and energy(as indicated by hatching between the curves 48 and 59 of FIG. 4).Consequently, if the means for disengaging the clutch includes aservomotor, the bulk, complexity and energy requirements of suchservomotor are well below those of a servomotor which must be put to useif the energy storing element 31 or its equivalent(s) is or are omitted.

The relative positions of various constituents of the friction clutch 1which is shown in FIGS. 1 and 2 correspond to those when the clutch isnew or prior to development of appreciable wear upon the frictionlinings 7 and certain other parts (such as 2, 3, 4 and 6). When thefriction linings 7 have undergone a certain amount of wear, the positionof the pressure plate 3 is changed in a direction toward thecounterpressure plate 6. This, in turn, entails a change of the conicityof the clutch spring 4 and hence a change of the bias of the clutchspring upon the pressure plate. The clutch spring 4 is preferablydesigned and mounted in such a way that its bias upon the pressure plate3 increases in response to progressing wear upon the friction linings 7.

As the pressure plate 3 moves closer to the counterpressure plate 6, itchanges its position relative to the sleeve-like members 16 of thesensor elements 15. Furthermore, the clutch spring 4 acts upon thering-shaped element 20 which is thus caused to follow the axial movementof the pressure plate 3 in a direction away from the housing 2.Consequently, the ring-shaped element 20 moves axially and away from thesleeve-like members 16 through a distance which is proportional to theextent of wear at least upon the friction linings 7. The ring-shapedelement 20 retains its axial position relative to the pressure plate 3during engagement of the clutch 1 because it is biased by the clutchspring 4 which urges it toward the pressure plate. Moreover, and asalready pointed out hereinbefore, the wear compensating unit 13 isself-locking, i.e., it constitutes a barrier or locking means in thecourse of a clutch engaging operation as well as during actualengagement of the clutch to prevent any compensation for wear duringsuch stages of actual use of the clutch.

During disengagement of the clutch,. i.e., when the pressure plate 3 isfree to move axially and away from the counterpressure plate 6 under thebias of the leaf springs (209), the pressure plate approaches thehousing 2 to the extent determined by the stop or stops 29. The axialposition of the ring-shaped element 20 relative to the pressure plate 3remains unchanged during axial movement of the pressure plate toward thestop or stops 29. As the disengagement of the clutch continues, thepressure plate 3 remains arrested by the stop or stops 29 but thering-shaped element 20 is then free to turn to the extent determined bycontinued axial movement of the radially outer portion 4a of the clutchspring 4 at the radius 38. Such angular movement of the element 20 isterminated when the element 20 reaches the sleeve-like members 16 of thesensor elements 15. If the axial (actually pivotal) movement of theclutch spring 4 continues in a direction to move its portion 4a awayfrom the pressure plate 3, the portion 4a also moves away from thering-shaped member 20 because the latter is arrested by the sleeve-likemembers 16. Such (even very minor) axial disengagement of the clutchspring 4 from the ring-shaped element 20 is of particular advantage forproper operation of the wear compensating means 12.

The wear compensating means 12 ensures that no compensation for wearwill take place if the tips 4c of the prongs 4b forming part of theclutch spring 4 move beyond their expected axial positions duringengagement of the clutch and that no compensation can take place if theclutch spring 4 happens to perform vibratory movements in the axialdirection of the housing 2.

Another advantage of the wear compensating means 12 is that it preventsany changes, or any appreciable changes, of the force-to-distancecharacteristics of the clutch spring 4 and the energy storing element 31during the entire useful life of the clutch. Thus, the stressing of theclutch spring 4 and/or of the element 31 does not change in the engagedcondition of the clutch irrespective of the (compensated) wear upon thefriction linings 7. This, in turn, ensures that the bias upon thepressure plate 3 as well as the progress of the disengaging forceremains at least substantially unchanged during the life span of theclutch.

The energy storing element 31 or its equivalent(s) can be utilized withequal or similar advantage in many other types of friction clutcheswhich are equipped with wear compensating means, namely with means whichcan compensate for wear at least upon the friction linings of the clutchdisc. By way of example only, friction clutches which are provided withwear compensating means are disclosed in published German patentapplications Nos. 42 39 389, 42 39 291, 43 06 505 and 43 22 677 as wellas in at least some of the references which are cited in such publishedapplications. Also by way of example only, a manually adjustable wearcompensating means for use in clutches is disclosed in U.S. Pat. No.4,832,164.

It is also possible to utilize in the friction clutch of FIGS. 1 and 2(or in an analogous clutch) an energy storing element 31 (or anequivalent of such element) which is installed in such a way that itexhibits a negative minimum of force when the clutch is engaged, i.e.,that the element 31 or its equivalent biases the pressure plate 3 towardthe counterpressure plate 6 when the clutch is engaged. Morespecifically, the element 31 then bears against the pressure plate 3through the medium of the clutch spring 4.

In order to prevent the energy storing element (diaphragm spring) 31from changing its orientation (namely from snapping over) relative tothe clutch spring 4, the clutch of FIGS. 1 and 2 would have to beprovided with suitable distancing means (not specifically shown) whichwould prevent a movement of the tips of the tongues 33 toward theadjacent portions of the prongs 4b of the clutch spring 4. Suchdistancing means would be installed in the clearances or gaps 36a one ofwhich is shown in FIG. 1. Alternatively, it would be possible to installsprings which would operate between the clutch spring 4 and the energystoring element 31; for example, such springs could be installed in theclearances 36a, i.e., in the regions where the tongues 33 abut therespective rivet heads 36, and would serve to bias the tongues 33against the adjacent heads 36. However, the springs which would be usedto bias the tongues 33 against the adjacent rivet heads 36 would have tobe stressed when the energy storing element 31 would be caused to movebeyond its unstressed position. This would entail an increase of thedisengaging force as a result of additional tilting of the element 31 aswell as due to the need to stress (compress) the springs between thetongues 33 and the adjacent rivet heads 36.

If a rise of the disengaging force during the last stage or portion ofthe movement of the bearing 39 in the direction of the arrow 37 (i.e.,to disengage the friction clutch 1) is not desired, the clutch can beequipped with a so-called compensation spring which equalizes or levelsthe progress of the disengaging force. Compensation springs which can beutilized in the clutch of FIGS. 1 and 2 (or in analogous clutches) aredisclosed, for example, in German patent application Serial No. P 43 17586.4.

A clutch which is equipped with the wear compensating means 12 oranalogous automatic wear compensating means must be further providedwith means for maintaining the wear compensating means in its startingor retracted position not only during transport but also duringinstallation of the clutch in the power train of a motor vehicle. Suchmaintaining means can or must be removed, dismantled or deactivated whenthe clutch is properly installed in the power train. For example, themaintaining means can be deactivated in automatic response to initialactuation of the clutch, e.g., in response to the action of centrifugalforce when the counterpressure plate 6 receives torque from the primemover for the very first time. Maintaining means of the above outlinedcharacter are disclosed in the above enumerated pending patentapplications.

A presently preferred maintaining means can be designed to ensure thatat least one constituent of the wear compensating means 12 (or analogouswear compensating means) which must be free to move in actual use of thewear compensating means is prevented from carrying out such movementduring transport and during installation of the clutch. For example, itis possible to maintain the ring-shaped element 20 in a predeterminedangular position relative to the housing 2 and/or to maintain the clutchspring 4 in a predetermined axial position relative to the adjoiningparts and/or to maintain the pressure plate 3 in a predetermined axialposition until after the installation of the clutch in a power train iscompleted. This ensures that the condition of the wear compensatingmeans 12 or analogous wear compensating means upon completion ofinstallation invariably corresponds to that condition which the wearcompensating means must assume prior to initial adjustment to compensatefor wear upon the friction linings 7 and, if necessary, for wear uponone or more additional parts of the clutch.

The various curves in the diagrams of FIGS. 3 and 4 are indicative ofthe characteristics of a single set of cooperating energy storingelements including the clutch spring 4, the resilient segments 10 andthe element 31. However, it is clear that the improved friction clutchcan embody other combinations of such or analogous energy storingelements without departing from the spirit of the invention. Forexample, it is possible to combine the various energy storing elementsin such a way that they generate negative forces during disengagement ofthe clutch. With reference to the diagram of FIG. 4, this would meanthat at least a portion of the curve 59 would extend below the abscissa.Thus, it would be necessary to forcibly disengage the clutch while thebearing 39 covers a certain portion of the overall distance 49 in thedirection of the arrow 37. However, this would present no problemsbecause the required disengaging force would be small, or extremelysmall, so that it could be readily furnished by a small electric motoror another suitable servomotor.

It is further possible to design the clutch in such a way that theenergy storing element 31 assists the clutch spring 4 in maintaining theclutch in the engaged condition. Thus, the initial stage of eachdisengagement of the clutch then involves a movement of the pressureplate 3 axially and away from the counterpressure plate 6 against theresistance of the energy storing element 31, i.e., the element 31 mustbe tilted to change its conicity in order to be in a position to furnisha force which assists the disengagement of the clutch.

The friction clutch 1 of FIGS. 1 and 2 is a pull type clutch, i.e., thebearing 39 must pull the tips 4c of the prongs 4b in the direction ofthe arrow 37 in order to effect a disengagement of the clutch. Theposition of the clutch spring 4 remains unchanged during the entireuseful life of the clutch and this, in turn, ensures that therelationship of the clutch spring 4 and the energy storing element 31 toeach other also remains at least substantially unchanged during the lifeof the clutch.

The situation is different in so-called push type clutches. A portion ofone such push type clutch 101 is shown in FIGS. 5 and 6. Since theclutch 101 is provided with wear compensating means 112 and such wearcompensating means employs one or more force monitoring sensors, theposition of the clutch spring 104 (shown in the form of a diaphragmspring) changes relative to the adjacent parts of the clutch. Morespecifically, the clutch spring 104 is caused to move axially relativeto the housing 102 and the pressure plate 103 of the push type clutch101. Therefore, it is necessary to ensure that the servo element 131(shown in the form of a diaphragm spring) also changes its position asthe wear upon the friction linings 107 of the clutch disc 108 progressesin order to ensure that the mode of cooperation between the clutchspring 104 and the element 131 remains unchanged.

The clutch spring 104 is installed in stressed condition between thehousing 102 and the pressure plate 103 of the friction clutch 101. Acircumferentially complete radially outer portion of the clutch spring104 bears upon the adjacent projections of the pressure plate 103. Thehousing 102 is non-rotatably connected to a counterpressure plate (notshown in FIGS. 5 and 6) which can receive torque from a suitable primemover in the same way as described with reference to the counterpressureplate 6 of FIGS. 1 and 2. The pressure plate 103 is non-rotatably butaxially movably coupled to the housing 102 and/or to the counterpressureplate in a manner not shown in FIGS. 5 and 6, e.g., by leaf springscorresponding to those shown at 209 in FIG. 9.

The clutch spring 104 can be said to constitute a two-armed lever whichis fulcrumed by a seat assembly 105 radially inwardly of the locus ofengagement of the clutch spring with the pressure plate 103.

The seat assembly 105 includes or cooperates with a stressed energystoring element 106 shown in the form of a diaphragm spring which reactsagainst the housing 102 and includes tongues or arms 106a bearingagainst that side of the clutch spring 104 which confronts the pressureplate 103. The axial force which the spring 106 applies to the clutchspring 104 is selected in such a way that it exceeds the disengagingforces which are normally required to disengage the clutch 101 and areapplied to the tips 110 of the radially inwardly extending prongs 111forming part of the spring 104. The spring 106 performs the function ofa sensor which ensures that, during normal disengagement of the clutch101 (i.e., during normal tilting of the spring 104 at the seat assembly105), the circumferentially complete radially outer portion of thespring 104 applies a predetermined axial force against an abutment 109at the inner side of the bottom wall of the housing 102.

The abutment 109 forms part of the wear compensating means 112, and thelatter further includes the sensor spring 106. The purpose of the wearcompensating means 112 is to change the axial position of the clutchspring 104 relative to the housing 102 to an extent corresponding to theextent of wear at least upon the friction linings 107 of the clutch disc108. Of course, the wear compensating means can be designed in such away that it compensates for wear upon the friction linings 107 as wellas upon one or more other parts which are likely to or which undergo atleast some wear during the useful life of the clutch 101. Such otherparts can include, for example, the pressure plate 103 and/or theaforementioned (not illustrated) counterpressure plate.

The wear compensating means 112 further comprises an annular member 113which can be said to constitute a wear compensating ring. To this end,the member 113 comprises an annulus of ramps which extend in thecircumferential direction of the pressure plate 103 and cooperate withcomplementary ramps provided at the inner side of the bottom wall of thehousing 102. The manner in which the ramps of the member 113 cooperatewith the ramps of the housing 102 is or can be similar, identical oranalogous to that described in connection with the ramps 22, 23 of thewear compensating means 12 shown in FIGS. 1 and 2. The wear compensatingmeans 112 still further comprises a second annular member 114 which isalso provided with circumferentially extending ramps cooperating withramps provided at the inner side of the bottom wall of the housing 102.

The circumferentially complete radially outer portion of the energystoring element 131 bears against the second annular member 114 of thewear compensating means 112. The tongues constituting the radially innerportion of the energy storing element 131 abut the adjacent prongs 111of the clutch spring 104.

The annular members 113, 114 are biased in the circumferential directionof the pressure plate 103 by resilient elements in the form of coilsprings 115, 116. The arrangement is such that the annular members 113,114 are installed to operate in series and the annular member 113constitutes a brake for the annular member 114. More specifically, theannular member 113 serves to prevent uncontrolled angular movements ofthe annular member 114 relative to the housing 102. As can be seen inFIG. 6, the members 113, 114 are provided with radially extendingprojections 113a, 114a which cooperate to prevent further angularmovement of the member 114 relative to the member 113 in acounterclockwise direction, as viewed in FIG. 6. The annular member 114and the coil spring(s) 116 (reacting against the housing 102 and bearingagainst the member 114) cooperate to ensure that the axial position ofthe energy storing element 131 is changed in response to changes of theaxial position of the clutch spring 104 relative to the housing 102,i.e., those changes in the axial position of the clutch spring 104 whichare necessary in view of the progessing wear upon the friction linings107. Each axial displacement of the clutch spring 104 entails an angularmovement of the annular member 113 through a distance which is afunction of the extent of wear upon the friction linings 107 (or of theextent of wear subsequent to the preceding compensation for such wear).The annular member 113 can turn relative to the housing 102 duringdisengagement of the clutch 101; at such time, the energy storingelement 131 exerts an axially oriented force upon the annular member 114so that the latter is (temporarily) held against rotation relative tothe housing 102. During such stage of disengagement, the projection orprojections 113a of the annular member 113 moves or move away from theprojection(s) 114a of the annular member 114. During the next-followingengagement of the clutch 101, the clutch spring 104 reassumes theorientation (conicity) which is shown in FIG. 5, and this entails astressing of the energy storing element 131. This, in turn, entails adrop of axial force which is furnished by the energy storing element131; this axially oriented force can be reduced to a minimum value oreven to zero. Therefore, the prestressed spring or springs 116 can turnthe annular member 114 relative to the housing 102 until theprojection(s) 114a catch up and abuts or abut the projection(s) 113a ofthe annular member 113. This ensures that the energy storing element 131completes the required axial movement as determined by the axialdisplacement of the clutch spring 104, and the thus axially adjustedelement 131 is also subjected to the same stress as before.

The construction and the mode of operation of the wear compensatingmeans 112 in the friction clutch 101 are or can be similar, identical oranalogous to those disclosed in the published German patent applicationsSerial Nos. 42 39 291 and 42 39 289. The disclosures of these Germanpatent applications, as well as of all previously enumerated Germanpatent applications (or of the corresponding pending United Statespatent applications and/or United States patents) are also incorporatedherein by reference.

FIGS. 7 and 8 illustrate a portion of another push type friction clutchwherein the annular member 114 of the wear compensating means 112 ofFIGS. 5 and 6 is incorporated into an energy storing element 231' whichfurther performs the functions of the element 131. The element 231' isbasically a diaphragm spring having a circumferentially complete annularradially outer portion and radially inwardly extending prongs. Theradially outer portion of the element 231' is provided with ramps 214'which cooperate with complementary ramps at the inner side of the bottomwall of the housing 202' of the friction clutch of FIGS. 7 and 8. Theramps 214' are of one piece with the element 231' and are obtained byshifting selected sections from the general plane of the radially outerportion of such element. The non-referenced complementary ramps can beof one piece with the bottom wall of the housing 202'. However, it isequally within the purview of the invention to employ separatelyproduced ramps 214' which are welded, riveted or otherwise affixed tothe energy storing element 231' and/or to employ separately producedcomplementary ramps which are welded, riveted and/or otherwise affixedto the bottom wall of the housing 202'.

The ramps 214' further perform the function of the projections 114ashown in FIG. 6 in that they cooperate with projections 213a' of theannular member 213' forming part of the wear compensating means in theclutch of FIGS. 7 and 8. FIG. 8 further shows energy storing elements inthe form of coil springs 215', 216' which respectively bias the annularmember 213' and the element 231' in the circumferential direction of thehousing 202'. The wear compensating action is carried in a mannerclearly analogous to that described for the wear compensating means 112in the friction clutch 101 of FIGS. 5 and 6. The main difference betweenthe wear compensating means 112 and the wear compensating meansincluding the structure shown in FIGS. 7 and 8 is that the energystoring element 231' can be rotated relative to the housing 202' as wellas relative to the clutch spring 204'.

FIG. 9 shows a push type friction clutch 201 having a housing or cover202 which is is fixedly secured to a rotary counterpressure plate 206 byscrews, bolts or other suitable threaded or unthreaded fasteners. Theradially outer portion of the counterpressure plate 206 carries astarter gear and its central portion is bolted and/or otherwise affixedto the output element (e.g., a camshaft or a crankshaft) of a primemover (such as a combustion engine in a motor vehicle).

The clutch 201 further comprises a pressure plate 203 which isnon-rotatably affixed to the housing 202 by leaf springs 209 so that ithas some freedom of movement in the direction of the common axis X--X ofthe housing and the counterpressure plate 206. When the clutch 201 isengaged, the pressure plate 203 is biased by a clutch spring 204 (shownin FIG. 9 in the form of a diaphragm spring) which causes theconfronting sides or faces of the plates 203, 206 to remain in requisitefrictional contact with the external surfaces of the respective frictionlinings 207 forming part of a clutch disc or clutch plate 208. Thelatter further comprises resilient segments 210 which are installedbetween the friction linings and perform or can perform the samefunctions as the resilient segments 10 in the friction clutch 1 of FIGS.1 and 2.

The clutch spring 204 is tiltable relative to a seat assembly 205 whichis carried by the housing 202. The leaf springs 209 extend substantiallytangentially of the clutch spring 204 and their end portions areriveted, bolted or otherwise secured to the adjacent portions of thepressure plate 203 and housing 202. The resilient segments 210 of theclutch disc 208 render it possible to achieve a progressive increase ofthe torque which is being transmitted by the counterpressure plate 206to the clutch disc 208 during engagement of the friction clutch 201.These resilient segments are flattened, and are thus caused to storeenergy or to store additional energy, when the pressure plate 203 ismoved in the direction of the axis X--X toward the counterpressure plate206 so that the friction linings 207 are caused to move axially andtoward each other to thus cause the segments 210 to undergo at leastsome deformation.

The assembly 205 comprises two seats 211, 212 flanking thecircumferentially complete radially outer portion of the clutch spring204. The regions of contact between the clutch spring 204 and theprojections at the right-hand side of the pressure plate 203 are locatedradially outwardly of the seat assembly 205. The seat 211 is analogousto the energy storing axially stressed member 106 of the wearcompensating means 112 shown in FIGS. 5 and 6; this seat biases theadjacent portion of the clutch spring 204 in the direction of the axisX--X and toward the inner side of the bottom wall of the housing 202.The seat 211 of FIG. 9 includes or constitutes a diaphragm spring 213 ora part which acts not unlike a diaphragm spring.

The other seat 212 of the assembly 205 is mounted on the housing 202 byway of wear compensating means 216. One of the purposes of the wearcompensating means 216 is to ensure that, when the seats 211, 212 arecaused to move in the direction of the axis X--X toward the pressureplate 203 and the counterpressure plate 206, no undesirable clearance orplay will develop between the seat 212 and the housing 202 and/orbetween the seat 212 and the clutch spring 204.

The friction clutch 201 (or the torque transmitting apparatus includingthe clutch 201) further comprises an adjusting unit 220 which ensuresthat the bias reducing means including the prongs 204b of the clutchspring 204 can be actuated (pushed in the direction of the axis X--X)without any play so that they can be repeatedly moved through identicaldistances in order to disengage the friction clutch 201. The adjustingunit 220 is installed between a release (pusher) bearing 220a (whichalso forms part of the bias reducing means) and the prongs 204b.

The exact details of friction clutches corresponding to the frictionclutch 201 of FIG. 9, of wear compensating means which can be utilized(as the means 216) in the clutch 201, and of an adjusting unit (whichcan be used as or in lieu of the adjusting unit 220) are disclosed inseveral aforementioned patents and/or applications. Reference may be hadin particular to the aforementioned published German patent applicationSerial No. 43 22 677.

The clutch 201 further comprises an energy storing element 231 which isa diaphragm spring installed between the housing 202 and an axiallymovable member 230 of the adjusting unit 220. The member 230 is part ofa ring which serves as a means for limiting the extent of axialmovability of the free end portions or tips of prongs 204b forming partof the clutch spring 204. The energy storing element 231 serves totransmit a clutch disengaging force and its radially inner portion istiltably mounted on the ring including the member 230 and bears againstthe latter in the direction of the axis X--X. The radially outer portionof the energy storing element 231 abuts against the housing 202 in thedirection of the axis X--X and is tiltable relative to the housing.

The conicity of the energy storing element 231 changes when the clutch201 is being disengaged, i.e., when the bearing 220a is moved toward thecounterpressure plate 206. The manner in which the force which isgenerated by the energy storing element 231 assists in disengagement ofthe clutch 201 is analogous to that described for the energy storingelement 31 of FIGS. 1 and 2 in connection with the diagrams of FIGS. 3and 4. The force which is furnished by the element 231 assists thedisengagement of the clutch 201 at least during a certain portion orstage of disengagement. At such time, the element 231 bears against thering including the member 230 in the direction of the axis X--X, and thering including the member 230 transmits such force to the tips of theprongs 204b forming part of the clutch spring 204.

A compensating ring 230a is installed between the ring including themember 230 and the clutch spring 204 to compensate for axialdisplacement of the clutch spring.

In those embodiments of the improved clutch which are shown in FIGS.1-2, 5-6, 7-8 and 9, the energy storing elements 31, 131, 231' and 231are installed in or are directly combined with or integrated into therespective friction clutches. However, it is equally possible to employone or more springs or like parts which perform the function of theenergy storing element 31, 131, 231' or 231 and are not installed in orincorporated into the respective friction clutches. For example, anenergy storing element which assists in disengagement of the clutch canbe installed in or combined with the clutch disengaging mechanism,namely a mechanism including that part or those parts which initiate thedisengagement of the clutch by applying forces to certain constituentsof the clutch proper, such as to the prongs 4b of the clutch spring 4 inthe clutch 1 of FIGS. 1 and 2. The disengaging mechanism or unit caninclude any one or any two or more of a number of different components,for example, at least one, two or more of the parts including mastercylinders, slave cylinders, disengaging bearings, fluid-operated(hydraulic or pneumatic) adjusters, electric motors, motion transmittinglinkages, motion or power transmitting conduits and/or conductors,Bowden wires, actuating levers, and/or depressible and/or otherwisemovable pedals.

All of the illustrated and/or otherwise described embodiments of theimproved friction clutch exhibit the advantage that they overcome atleast some drawbacks of heretofore known friction clutches regarding thefacility, accuracy, predictability and reproducibility of disengagementduring the entire useful life of such clutches. Thus, the improvedfriction clutch is designed and assembled in such a way that it can bedisengaged in response to the application of relatively small forces (atleast during a substantial portion or stage of the disengagingoperation) and/or that the magnitude of the disengaging force remains atleast substantially constant or fluctuates within a surprisingly narrowrange in the course of the entire disengaging operation or at leastduring a substantial part of such operation. The disengaging force to beapplied need not exhibit any pronounced peaks and the ratio of themaximum required disengaging force to the minimum disengaging force ismuch lower than in connection with the manipulation of conventionalfriction clutches; as a rule, such ratio does not exceed and can be muchless than 1.5. All of the above outlined advantages can be achieved byresorting to a relatively simple, compact, inexpensive and durablefriction clutch.

It is further within the purview of the invention to employ manuallyoperable wear compensating means to be actuated from time to time inorder to compensate for wear upon the friction linings of the clutchdisc but preferably also for wear upon the pressure plate, thecounterpressure plate, the clutch spring and/or the housing of thefriction clutch. However, the automatically operated wear compensatingmeans are preferred because they need not be attended to during theentire life span of the clutch.

If the clutch spring of the improved friction clutch is a diaphragmspring and the energy storing element performing the function of theelement 31, 131, 231' or 231 is also a diaphragm spring, the energystoring element can resemble but can be weaker than the clutch spring.

If the resilient segments 10 or 210 or their equivalents are omitted,i.e., if no such segments are built into the clutch disc proper, thefriction clutch can employ functional equivalents of such segments atone or more other locations rather than between the friction linings.For example, functional equivalents of the segments 10 or 210 can beinstalled to operate between the clutch spring and the pressure plate.

The improved friction clutch is susceptible of numerous additionalmodifications without departing from the spirit of the invention. Forexample, the various features which are shown in FIGS. 1-2, 5-6, 7-8 and9 can be used interchangeably or in a number of combinations with eachother. Furthermore, the novel features of the illustrated andaforedescribed friction clutches can be incorporated in many types ofconventional clutches to thus enable the modified conventional clutchesto exhibit the aforediscussed advantages. Still further, applicantreserves the right to seek and obtain patent protection for combinationsof certain elements of the improved friction clutch and/or for certainindividual novel elements of such clutch. Additional novel andpatentable features are believed to reside in a method of enhancing theoperation of a friction clutch for the purpose of disengaging the clutchdisc or clutch plate from the pressure plate and the counterpressureplate in response to the application of relatively small disengagingforces and/or in response to the application of disengaging forces whichfluctuate within a narrow range (if at all).

Last but not least, the invention is believed to reside in the provisionof a torque transmitting apparatus which employs the aforedescribedfriction clutch or other friction clutches in conjunction with one ormore energy storing elements corresponding to the element 31, 131, 231'or 231, and/or in a combination of a friction clutch with a clutchdisengaging mechanism which employs one or more equivalents of theenergy storing element 31, 131, 231' or 231.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of the aboveoutlined contribution to the art and, therefore, such adaptations shouldand are intended to be comprehended within the meaning and range ofequivalence of the appended claims.

What is claimed is:
 1. An engageable and disengageable friction clutch,comprising a housing rotatable about a predetermined axis; means forrotating said housing including a counterpressure plate rotatable aboutsaid axis; a pressure plate coaxial and rotatable with and disposedbetween said housing and said counterpressure plate and movable in thedirection of said axis; a clutch disc coaxial with and disposed betweensaid plates and being subject to wear upon repeated progressingfrictional contact and progressing reduction of frictional contact withsaid plates in response to axial movement of said pressure plate towardand away from said counterpressure plate; means for engaging the clutchincluding at least one clutch spring arranged to bias said pressureplate against said clutch disc in the engaged condition of the clutch;means for reducing the bias of said at least one spring upon saidpressure plate to thus disengage the clutch; at least one at leasttemporarily stressed energy storing element operative in parallel withsaid at least one spring to generate forces promoting at least in partthe disengagement of the clutch; and means for automaticallycompensating for wear at least upon said clutch disc.
 2. The clutch ofclaim 1, wherein said pressure plate is movable within limits in thedirection of said axis and said counterpressure plate includes a partarranged to receive torque from a prime mover, said clutch discincluding friction linings which are subject to wear and are contactedby said plates in the engaged condition of the clutch.
 3. The clutch ofclaim 1, wherein said at least one energy storing element is constructedand installed to exhibit a progressive force-to-distance characteristicat least during a portion of movement of said pressure plate todisengage the clutch.
 4. The clutch of claim 1, wherein said at leastone energy storing element includes a diaphragm spring.
 5. The clutch ofclaim 1, wherein said at least one clutch spring includes a diaphragmspring.
 6. The clutch of claim 1, wherein said at least one clutchspring includes an annular portion and prongs extending from saidannular portion substantially toward said axis and forming part of saidmeans for reducing the bias of said at least one clutch spring upon saidpressure plate.
 7. The clutch of claim 1, wherein said at least oneclutch spring has a degressive force-to-distance characteristic at leastduring a portion of movement of said pressure plate away from saidcounterpressure plate.
 8. The clutch of claim 1, wherein said pressureplate covers a predetermined distance during movement away from saidcounterpressure plate to disengage the clutch and said distance includesa first portion and a second portion, said pressure plate applying tosaid clutch disc a decreasing force during movement through said firstportion of said distance and said clutch disc being spaced apart fromsaid plates during movement of said pressure plate through said secondportion of said distance, said at least one energy storing elementexhibiting a positive force-to-distance characteristic during movementof said pressure plate through said first portion of said distance. 9.The clutch of claim 8, wherein said at least one energy storing elementis operative to generate forces promoting the disengagement of theclutch during movement of said pressure plate through the entire firstportion of said predetermined distance.
 10. The clutch of claim 8,wherein said at least one energy storing element is operative togenerate forces tending to promote the disengagement of the clutchduring a part of movement of said pressure plate through said secondportion of said predetermined distance.
 11. The clutch of claim 1,wherein said at least one energy storing element bears, at leastindirectly, against one of said housing and said bias reducing means andreacts, at least indirectly, against the other of said housing and saidbias reducing means.
 12. The clutch of claim 1, wherein said at leastone energy storing element bears, at least indirectly, against one ofsaid housing and said at least one clutch spring and reacts, at leastindirectly, against the other of said housing and said at least oneclutch spring.
 13. The clutch of claim 1, wherein said at least oneenergy storing element is stressed in the engaged condition of theclutch without exerting an appreciable force in the direction of saidaxis.
 14. The clutch of claim 1, wherein said at least one energystoring element is stressed in the engaged condition of the clutch andexerts in the direction of said axis a force which increases at leastduring at least one stage of disengagement of the clutch.
 15. The clutchof claim 1, wherein said at least one energy storing element is arrangedto be subjected to a stress which varies between a maximum stress and aminimum stress, said at least one energy storing element having asubstantially sinusoidal force-to-distance characteristic curve andbeing subjected to a stress which is at least close to said minimumstress in the engaged condition of the clutch.
 16. The clutch of claim1, wherein said at least one energy storing element is stressed in theengaged condition of the clutch to generate a force in the direction ofsaid axis.
 17. The clutch of claim 1, wherein said clutch disc includesfirst and second friction linings which are contacted by said plates inthe engaged condition of the clutch, and are resilient means disposedbetween and urging said first and second friction linings away from eachother in the direction of said axis.
 18. The clutch of claim 1, whereinsaid at least one energy storing element comprises a diaphragm springand further comprising means for tiltably mounting said diaphragm springon said housing.
 19. The clutch of claim 18, wherein said diaphragmspring includes a radially outer portion which is tiltably mounted onsaid housing.
 20. The clutch of claim 1, wherein said at least oneenergy storing element includes a diaphragm spring having a radiallyinner portion acting upon said bias reducing means.
 21. An engageableand disengageable friction clutch, comprising a housing rotatable abouta predetermined axis; means for rotating said housing including acounterpressure plate rotatable about said axis; a pressure platecoaxial and rotatable with and disposed between said housing and saidcounterpressure plate and movable within limits in the direction of saidaxis; a clutch disc coaxial with and disposed between said plates andhaving friction linings subject to wear upon repreated progressingfrictional contact and progressing reduction of frictional contact withsaid plates in response to axial movement of said pressure plate towardand away from said counterpressure plate; means for moving said pressureplate including at least one first diaphragm spring arranged to biassaid pressure plate against said clutch disc in the engaged condition ofthe clutch; means for reducing the bias of said at least one firstdiaphragm spring upon said pressure plate to thus disengage the clutch;at least one stressed second diaphragm spring operative in parallel withsaid at least one first diaphragm spring to generate forces promoting atleast in part the disengagement of the clutch; and means forautomatically compensating for wear at least upon said friction linings,including means for adjusting the bias of said at least one firstdiaphragm spring upon said pressure plate.
 22. The clutch of claim 21,wherein said at least one second diaphragm spring is constructed andinstalled to exhibit a progressive force-to-distance characteristic atleast during a portion of movement of said pressure plate to disengagethe clutch.
 23. The clutch of claim 21, wherein said at least one firstdiaphragm spring comprises an annular portion and prongs extending fromsaid annular portion substantially toward said axis and forming part ofsaid means for reducing the bias of said at least one first diaphragmspring upon said pressure plate.
 24. The clutch of claim 21, whereinsaid at least one first diaphragm spring has a degressiveforce-to-distance characteristic at least during a portion of movementof said pressure plate away from said counterpressure plate.
 25. Theclutch of claim 21, wherein said pressure plate covers a predetermineddistance during movement away from said counterpressure plate todisengage the clutch and said distance includes a first portion and asecond portion, said pressure plate applying to said clutch disc adecreasing force during movement through said first portion of saiddistance and said clutch disc being spaced apart from said plates duringmovement of said pressure plate through said second portion of saiddistance, said at least one second diaphragm spring exhibiting apositive force-to-distance characteristic during movement of saidpressure plate through said first portion of said distance.
 26. Theclutch of claim 25, wherein said at least one second diaphragm spring isoperative to generate forces promoting the disengagement of the clutchduring movement of said pressure plate through the entire first portionof said distance.
 27. The clutch of claim 25, wherein said at least onesecond diaphragm spring is operative to generate forces tending topromote the disengagement of the clutch during a part of movement ofsaid pressure plate through said second portion of said distance. 28.The clutch of claim 21, wherein said at least one second diaphragmspring bears, at least indirectly, against one of said housing and saidbias reducing means and reacts, at least indirectly, against the otherof said housing and said bias reducing means.
 29. The clutch of claim21, wherein said at least one second diaphragm spring bears, at leastindirectly, against one of said housing and said at least one firstdiaphragm spring and reacts, at least indirectly, against the other ofsaid housing and said at least one first diaphragm spring.
 30. Theclutch of claim 21, wherein said at least one second diaphragm spring isstressed in the engaged condition of the clutch without exerting a forcein the direction of said axis.
 31. The clutch of claim 21, wherein saidat least one second diaphragm spring is stressed in the engagedcondition of the clutch and exerts in the direction of said axis a forcewhich increases at least during at least one stage of disengagement ofthe clutch.
 32. The clutch of claim 21, wherein said at least one seconddiaphragm spring is arranged to be subjected to a stress which variesbetween a maximum stress and a minimum stress, said at least one seconddiaphragm spring having a substantially sinusoidal force-to-distancecharacteristic curve and being subjected to a stress which is at leastclose to said minimum stress in the engaged condition of the clutch. 33.The clutch of claim 21, wherein said at least one second diaphragmspring is stressed in the engaged condition of the clutch to generate aforce in the direction of said axis.
 34. The clutch of claim 21, whereinsaid clutch disc further comprises resilient means disposed between andurging said friction linings away from each other in the direction ofsaid axis.
 35. The clutch of claim 21, further comprising means fortiltably mounting said at least one second diaphragm spring on saidhousing.
 36. The clutch of claim 35, wherein said at least one seconddiaphragm spring includes a radially outer portion which is tiltablymounted on said housing.
 37. The clutch of claim 21, wherein said atleast one second diaphragm spring includes a radially inner portionacting upon said bias reducing means.
 38. An engageable anddisengageable friction clutch, comprising a housing rotatable about apredetermined axis; means for rotating said housing including acounterpressure plate rotatable about said axis; a pressure platecoaxial and rotatable with and disposed between said housing and saidcounterpressure plate and movable within limits in the direction of saidaxis; a clutch disc coaxial with and disposed between said said platesand having friction linings subject to wear upon repeated progressingfrictional contact and progressing reduction of frictional contact withsaid plates in response to axial movement of said pressure plate towardand away from said counterpressure plate; means for moving said pressureplate including at least one first energy storing element arranged tobias said pressure plate against said clutch disc in the engagedcondition of the clutch; means for reducing the bias of said at leastone first energy storing element upon said pressure plate to thusdisengage the clutch; at least one second energy storing elementoperative in parallel with said at least one first energy storingelement to generate forces promoting the disengagement of the clutch;resilient means disposed between said friction linings and alsooperative to generate forces promoting the disengagement of the clutch;and means for automatically compensating for wear at least upon saidfriction linings.
 39. The clutch of claim 38, wherein said at least onesecond energy storing element is constructed and installed to exhibit aprogressive force-to-distance characteristic at least during a portionof movement of said pressure plate to disengage the clutch.
 40. Theclutch of claim 38, wherein said at least one second energy storingelement includes a diaphragm spring.
 41. The clutch of claim 38, whereinsaid at least one first energy storing element includes a diaphragmspring.
 42. The clutch of claim 38, wherein said at least one firstenergy storing element includes an annular portion and prongs extendingfrom said annular portion substantially toward said axis and formingpart of said means for reducing the bias of said at least one firstenergy storing element upon said pressure plate.
 43. The clutch of claim38, wherein said at least one first energy storing element has adegressive force-to-distance characteristic at least during a portion ofmovement of said pressure plate away from said counterpressure plate.44. The clutch of claim 38, wherein said pressure plate covers apredetermined distance during movement away from said counterpressureplate to disengage the clutch and said distance includes a first portionand a second portion, said pressure plate applying to said clutch disc adecreasing force during movement through said first portion of saiddistance and said clutch disc being spaced apart from said plates duringmovement of said pressure plate through said second portion of saiddistance, said at least one second energy storing element exhibiting apositive force-to-distance characteristic during movement of saidpressure plate through said first portion of said distance.
 45. Theclutch of claim 44, wherein said at least one second energy storingelement is operative to generate forces promoting the disengagement ofthe clutch during movement of said pressure plate through the entirefirst portion of said distance.
 46. The clutch of claim 44, wherein saidat least one second energy storing element is operative to generateforces tending to promote the disengagement of the clutch during a partof movement of said pressure plate through said second portion of saidpredetermined distance.
 47. The clutch of claim 38, wherein said atleast one second energy storing element bears, at least indirectly,against one of said housing and said bias reducing means and reacts, atleast indirectly, against the other of said housing and said biasreducing means.
 48. The clutch of claim 38, wherein said at least onesecond energy storing element bears, at least indirectly, against one ofsaid housing and said at least one first energy storing element andreacts, at least indirectly, against the other of said housing and saidat least one first energy storing element.
 49. The clutch of claim 38,wherein said at least one second energy storing element is stressed inthe engaged condition of the clutch without exerting any appreciableforce in the direction of said axis.
 50. The clutch of claim 38, whereinsaid at least one second energy storing element is stressed in theengaged condition of the clutch and exerts in the direction of said axisa force which increases at least during at least one stage ofdisengagement of the clutch.
 51. The clutch of claim 38, wherein said atleast one second energy storing element is arranged to be subjected to astress which varies between a maximum stress and a minimum stress, saidat least one second energy storing element having a substantiallysinusoidal force-to-distance characteristic curve and being subjected toa stress which is at least close to said minimum stress in the engagedcondition of the clutch.
 52. The clutch of claim 38, wherein said atleast one second energy storing element is stressed in the engagedcondition of the clutch to generate a force in the direction of saidaxis.
 53. The clutch of 38, wherein said resilient means includes atleast one spring which biases said friction linings away from each otherin the direction of said axis.
 54. The clutch of claim 38, wherein saidat least one second energy storing element comprises a diaphragm springand further comprising means for tiltably mounting said diaphragm springon said housing.
 55. The clutch of claim 54, wherein said diaphragmspring includes a radially outer portion which is tiltably mounted onsaid housing.
 56. The clutch of claim 38, wherein said at least onesecond energy storing element includes a diaphragm spring having aradially inner portion acting upon said bias reducing means.